The search for survivors on the world's second-tallest peak ended Tuesday, when the severely frostbitten Italian climber Marco Confortola made it to safety after 11 lives were lost in one of the most tragic accidents of modern mountaineering.

European and Korean teams were struck by a series of disastrous events during a summit attempt on K2, which straddles the Pakistan-China border and is considered one of the most difficult peaks to summit.

But unlike many recent mountain fatalities, often attributed to inexperienced climbers paying top dollar to climb "trophies" like Mt. Everest, these were seasoned mountaineers. In the aftermath, veteran climbers say the focus is likely to be on a possible breakdown in teamwork and whether unconfirmed media reports of fatalities jeopardize rescue attempts.

After a Friday ice avalanche, some climbers at the K2 base camp got on the telephone, prompting media reports of 11 "confirmed" deaths, long before they were in fact confirmed.

"The main danger with all this is if people read, all over the world [and] on CNN ... that 11 people are confirmed dead, the motivation for actually risking your life and going up there to rescue people stops," says Tom Sjogren, a founder of Explorersweb.com, who has himself been on the summit of Everest once during four climbs there. "I've never seen missing people actually be declared dead on such a scale.... But I've seen people declared dead and coming back after 4 to 5 days, even on K2."

Veteran climbers have long considered K2 one of the most treacherous mountains, a 28,240-foot high behemoth conquered only 281 times by mountaineers before Friday – compared to nearly 3,000 for Mt. Everest. Though 66 climbers had died on K2 as of last year, no more than six had been lost in a single event, according to Explorersweb.com.

"I think there were some tactical errors made, but it wasn't the tactics that killed them," says US climbing veteran Chris Warner, who led a successful expedition to K2 last year – among the latest of 140 career expeditions. "You can point and say: 'They got to the summit at 8 o'clock [in the dark].' That was a mistake, but it wasn't what killed them. You can say 'those people on oxygen probably ran out of oxygen.... But that's not what killed them. What killed them was the ice fall."

Two climbers, a Serb and a Pakistani, died on the summit attempt on Friday. It ran into further trouble when a European team led by Dutch climber Wilco van Rooijen found that safety ropes fixed at the narrow Bottleneck had been placed wrongly.

"We were astonished," Mr. van Rooijen told the Associated Press after being rescued by a Pakistani helicopter. "We had to move it. That took, of course, many, many hours. Some turned back because they didn't trust it anymore."

Many climbers made the summit. But a large chunk of ice – part of a 500-foot-tall glacier that permanently overhangs the Bottleneck – broke off, ripping out safety ropes along the gully as well as on an even more dangerous traverse along near-vertical ice. A number of climbers were trapped overnight in the high-altitude zone with little oxygen and temperatures of -40 degrees F.

Teamwork broke down

Daylight brought thick clouds that limited visibility and climbers couldn't find each other, van Rooijen said. Teamwork broke down. "People were running down but didn't know where to go, so a lot of people were lost on the mountain on the wrong side, wrong route, and then you have a big problem," he said. The Climbers made their way down, and some fell to their death trying, but other teams had not marked the route with flags to the tents at Camp Four as they had promised.

"Some climbers did not take their responsibility and then accidents like this happen very easy," said van Rooijen.

Colleagues in close touch with those on the mountain say the Dutch team was the first to arrive at the K2 base camp this season, in mid-May, and shouldered much of the burden of route setting and logistics.

"Wilco and his team ... were putting up all the fixed ropes, and other people were climbing on it," says Mr. Sjogren, who also runs a company supplying satellite and other technical equipment to expeditions.

That created some friction among the teams, Sjogren says. On summit day, van Rooijen's group was further delayed by climbing down to aid a fallen Serbian climber, only to find that he was dead.

The result was a nighttime summit on Friday, though the weather was exceptionally good.

"So it's a little hard to say: 'That was the wrong decision, you should have a [cutoff] time,' " says Sjorgen. "You really should have a cap of time. But sometimes things happen that make you change your decision.... This accident can't be put on the climbers, that they've been careless."

Mr. Warner agrees, saying though there were tactical errors, the determining factor was the ice fall. He knew a dozen of the climbers on the mountain this week, all of them "tremendously experienced."

Top climbers, not 'trophy hunters'

Many of the climbers on K2 this week – such as Norwegian climber Rolf Bae, who was swept away with the ice fall – were experienced polar explorers. Mr. Bae was on his second K2 climb, and in early June had completed a new route on Pakistan's Trango Tower face, spending 27 days on one of the biggest sheer rock walls in the world.

"This is the kind of climber we are talking about here," says Sjogren, noting that van Rooijen had summitted Mt. Everest before without bottled oxygen – a very rare feat. "These were not the trophy hunters, the first-time climbers. And none of them were on a commercial expedition."

But Reinhold Messner, the Italian climbing legend who first tackled all 14 peaks taller than 8,000 meters (26,250 feet), was critical. "People today are booking these K2 package deals almost as if they were buying some all-inclusive trip to Bangkok," he told a German television station. Reaching the summit after dark "is just pure stupidity; that is not professional."

Warner says that though the tragedy will raise the issue of commercial guiding, it didn't factor on K2 this time.

"Let's just pray that they were driven to climb [K2] by some deeply held personal goal and not for some external hope to become rich and famous," adds Warner. "The world is not going to be a better place because the 280th person summited K2. But hopefully they, as an individual, are better for it."